Optical multiplex or demultiplex devices based on echelle grating techniques have been used to realize multiplexing or demultiplexing of optical signals. Several approaches may be implemented to increase reflectivity of the grating surface in such devices and accordingly reduce optical loss. For example, metal may be deposited on the grating surface to enhance reflectivity. In another example, distributed Bragg reflector (DBR) mirrors may be fabricated behind the grating surface. In yet another example, straight grating facets may be replaced by corner mirror structures in the grating surface. However, these or similar approaches may be difficult to implement from a fabrication perspective and may cause implementation inaccuracy and integration problems, which may result in insufficient reflectivity increase.